Complex sentence: The majority of math teaching fellows attend the session of Math Immersion training, which takes place in the two weeks prior to regular pre-service training, where it covers the basic content of the CST and high school curriculum in their assigned subject area.
Split into simpler sentences: The majority of math Fellows attend the session of Math Immersion training that takes place during the two weeks prior to regular pre-service training. This additional training session where it covers the basic content of the CST and high school curriculum in their assigned subject area.