I noticed that boys sweat more than girls in the PE class performing same physical activity. Is there any other specific reason except muscle mass?
Your assumption seems to be true that Males sweat more than Females, but, not necessarily because of muscle mass. The jury is still out as to the reasons. However, in a 2010 study, it was concluded that…
… training improved the sweating response, and a sex difference was observed in the degree of improvement in the sweating response due to physical training. This sex difference became more pronounced with increasing exercise intensity. A sex difference was observed in the control of sweating rate to an increase in exercise intensity, i.e. the maximal activated sweat gland responses of untrained females required a higher body temperature or work intensity than the other groups.
So, there does seem to be something different in the way males and females sweat. Recent research suggests
that when we're under heat stress from high temperatures or an intense workout -- regardless of what shape we're in or how much body fat we have -- women consistently sweat less than men but tend to have a higher skin temperature.
In a nutshell, the cause(s) for the differences in how men and women sweat is still unknown. Some think it may have to do with body composition. While others think more research is required to determine
how efficiently we use the sweat we produce, but also to our capacity for making sweat, hormonal fluctuations, sex hormone differences and how our bodies regulate water as possible reasons why men sweat more than women.