High School More Class Mates 4.8.1  

increasing the number of students from 8 to 27 + the 5 special ones to alltogether 32 class mates.
(the size of my class when I went ... :-) before they split us)

16 go to class 1, 16 to the other class.

Remember to raise your maximum sims on lot value from 20 to 40 via MCCC or similar. (For me more than 40 starts lagging)
Or use the file in the optional files section if you do not want to use MCCC.

Can be easily adopted with S4Studio for your needs. (I do not plan to launch versions of this)
=> See picture 1 and 2. 

To increase or decrease the total amount change the 27 for lower and upper bound in:
weeklySchedule_HighSchool_Active_Main, 
weeklySchedule_HighSchool_Active_CareerDay
weeklySchedule_HighSchool_Active_FireDrill

How many go to class 1 depends on the numbers for upper limit (16) in the records:
situationData_HighSchool_Active_NPC_GoToClass1_WithTrait
situationData_HighSchool_Active_NPC_GoToClass1_NoTrait
situationData_HighSchool_Active_NPC_AttendClass1_WithTrait
situationData_HighSchool_Active_NPC_AttendClass1_NoTrait

The rest than goes to class 2 till the upper limit (18) in
situationData_HighSchool_Active_Background_GoToClass_Others
situationData_HighSchool_Active_Background_AttendClass_Others
is reached.

Others will hang around somewhere else in the school.