It is usual for foreign teachers to work with whole classes, on average around 40-50 students, although it can be higher than this. You will be invited to contribute your own ideas as well as follow set courses.
The school day starts around 8am in Lesotho (for Primary Schools, from 8:30am in winter) and ends at 2pm for Primary Schools and 4pm for Secondary. Classes run from Monday to Friday and you will be expected to help with occasional extra-curricular activities after school or on some weekends according to your own interests. What subject you will teach will depend on your own skills and abilities, and whether you are a Primary or Secondary school teacher.
All teachers however will be expected to teach some English and possibly Maths. Your timetable can be negotiated with your school after your arrival. Teachers will also be expected to undertake some workshops and trainings in order to share their skills with others.