Information on this under-researched topic was presented in a paper based on the MTA study (Abikoff, et al., (2002). Observed classroom behavior of children with ADHD: Relationship to gender and comorbidity. Journal of Abnormal Child Psychology, 30, 349-359).

Participants in this observational study were 502 7-10 year old children diagnosed with ADHD, Combined Type (403 boys and 99 girls) recruited at all 6 study sites. The results reported below thus reflect observations that occurred in many classrooms in multiple regions of the country.

Children were observed on two separate occasions in their classroom by trained observers. Each observation period lasted 16 minutes. (Note: For approximately 10% of children, only a single 16-minute observation was conducted). For each child with ADHD observed, a classmate of the same gender and ethnicity as the ADHD child was observed. This comparison child was identified by the teacher as a "typical classmate," i.e. no excessive behavior problems but not the best-behaved student either.

Observations occurred during teacher-led lessons and/or independent academic seatwork time under teacher supervision and observers were informed about specific classroom rules prior to the observation. All children had been diagnosed relatively recently, and observations were conducted prior to the start of either medical and/or behavioral treatment provided in the study. To keep observations from being biased, observers did not know which children had been diagnosed with ADHD and which were comparison children.

Each ADHD student and his/her comparison child were observed in 4 alternating 4-minute blocks, yielding 16 minutes of data on each child. During this time, observers were trained to note the occurrence of the following behaviors: interference (e.g., clowning, interrupting others, talking during work), interference to teacher (e.g. interrupting teacher), off-task (sustained inattention or distractibility), noncompliance (not complying with teacher requests or instructions), aggression (physical aggression or destruction of property), verbal aggression to children (e.g., name calling, taunting, teasing), verbal aggression to teacher (e.g. name calling, arguing), minor motor movement (e.g. rocking in seat), gross motor - vigorous (e.g., running, skipping), out-of-chair (extended time out of seat), and solicitation (e.g. going up to teacher, calling out to teacher).

In addition to these individual behavior codes, two composite scores were calculated: the two gross motor categories were combined to yield a composite gross motor score, and, an overall ADHD composite was obtained by summing scores for interference, interference to teacher, off task, and the gross motor composite.

As noted above, nearly all children were observed twice, resulting in 32 minutes of data for over 90% of the sample. Observation periods were divided into 15-second intervals, and the initial occurrence of each behavior observed during the interval was recorded. Thus, multiple behaviors could be recorded for a single interval, but each behavior would be counted only once per interval. Off-task, non-compliance and out-of-chair behaviors had to be observed for the entire 15-second interval to be recorded. When none of the problem behaviors occurred during an interval, the code "absence of behavior" was recorded.

Summary scores were derived for each behavior by calculating the percentage of intervals in which it was observed. For example, 32 minutes of observation translates into 128 15-second intervals. If a child were off-task during 22 of those intervals, his off-task score would be 22 divided by 128 or 17%.

RESULTS

BOYS VERSUS GIRLS

The researchers first compared behaviors for boys and girls overall, irrespective of ADHD status. Boys had significantly higher rates of observed interference, and also had higher scores on the gross motor composite and ADHD composite. Differences on other behaviors were consistently higher for boys, but were not statistically significant.

ADHD BOYS VERSUS COMPARISON BOYS

ADHD boys had higher observed rates of all behaviors coded than comparison boys except for solicitation of the teacher. To put these differences in context, behaviors comprising the ADHD composite (i.e. interference, interference to teacher, off task, gross motor - standing, and gross motor - vigorous) were observed in 38% of the intervals for ADHD boys versus 15% of the intervals for comparison boys. Non-compliance and aggressive behavior was observed to occur infrequently in both groups, but was still more common for ADHD boys than comparison boys (i.e. 2.4% vs. .3% for non-compliance; .5% vs. .1% for physical aggression; .9% vs. .3% for verbal aggression). One reason why frequency of aggressive behavior may have been so low is that all observations occurred in structured classroom settings. In less supervised settings (e.g. lunch room, playground) the occurrence of aggression would likely have been greater.

ADHD GIRLS VERSUS COMPARISON GIRLS

Girls with ADHD differed with comparison girls on all but three of the behavior categories (i.e. physical aggression, verbal aggression to teacher, and out-of-seat behavior). Behaviors comprising the ADHD composite were observed in 25% of the intervals for ADHD girls versus 11% of intervals for comparison girls.

ADHD BOYS VERSUS ADHD GIRLS

Compared to girls with ADHD, boys with ADHD had significantly higher rates of interference (21.4% of intervals vs. 12.5), total aggression (1.9% vs. .9%), gross motor composite (3.5% vs. 2.3%), and the ADHD composite (38% vs. 25%).

EFFECT OF COMORBID PROBLEMS

In addition to examining behavior differences in relation to ADHD status and gender, the authors also examined whether comorbid behavior disorders (i.e. an additional diagnosis of either oppositional defiant disorder (ODD) or conduct disorder (CD) or an anxiety disorder related to classroom behavior. Of the entire sample of children with ADHD, approximately 12% had ADHD + anxiety, 34% had ADHD + ODD/CD, 22% had ADHD + anxiety + ODD/CD, and 33% had ADHD alone.

Compared to children with ADHD alone, those with ADHD and anxiety did not show significant differences on any of the observed behaviors. When ODD or CD was present in addition to ADHD, however, higher rates of interference, off-task behavior, verbal aggression to teacher, total aggression, and the ADHD composite were all significantly higher than for children with ADHD alone.

SUMMARY AND IMPLICATIONS

Results from this study reveal a wide range of differences in classroom behavior between children with and without ADHD. Of particular interest were the clear differences observed between ADHD boys and girls. ADHD girls had significantly lower scores than ADHD boys on the ADHD composite index. They also showed less disruptive, rule-breaking behaviors than boys with ADHD, as exemplified by rates of interference and total aggression that were approximately half those of their male counterparts.

These findings have potentially important implications for identification and diagnosis. Because girls with ADHD will generally be less overtly symptomatic, disruptive, and aggressive than boys with ADHD - even when they have been diagnosed with the combined subtype - they are likely to be experienced as less problematic by their teachers. In fact, in addition to being less aggressive than boys with ADHD, girls with ADHD were no more aggressive or likely to be out of their seat than girls without ADHD. As a result, teachers may be less likely to pick up on these girls' difficulties. In many instances, this could result in being identified much later than boys, or to never being identified at all.

The problem with this is that the longer ADHD goes untreated, the more likely it is to result in severely compromised academic performance as well as to the development of other difficulties. This is likely to be compounded by the fact that the inattentive subtype of ADHD may be more common in girls than boys, and overt behavior problems are less pronounced in children with this subtype. These observational findings highlight the need for teachers as well as clinicians to be aware of these gender-related differences and of their potential impact on the under identification and misdiagnosis of girls with ADHD.

Results from the comorbidity analyses are also interesting. What is clear from these results is that the presence of a disruptive behavior disorder is associated with even greater classroom behavioral impairment than is ADHD alone. These findings highlight the importance of preventing the development of these other difficulties in children with ADHD.

In summary, results from this study provide the first observational evidence of importance behavioral differences between boys and girls with ADHD. The nature of these differences is one that is likely to result in many cases of ADHD in girls being missed, or at least not diagnosed until substantially later than boys. Unfortunately, this would increase the likelihood of significant academic problems and other emotional and/or behavioral difficulties developing as a girl's core ADHD symptoms go untreated. Hopefully, information provided by studies such as this will reduced the frequency of such occurrences.