My courses I currently teach are mandated to be asynchronous by the college (there are other sections of the same course that are synchronous or blended so students have a choice ). So to compensate for the challenging, difficult concepts I hold study sessions and offer different days and times for students as it is optional, but have high attendance and positive feedback. This also leads to a question and answer session. Students come enter or exit the study session (usually 2 hours) as they wish.
