After a significant number of students have demonstrated their ability to measure their heart rate, the class will begin independent practice.
(a significant number of students; have demonstrated; their ability to measure their heart rate) (the class; will begin; independent practice; T:After a significant number of students have demonstrated their ability)
a significant number of students the class
have demonstrated will begin
their ability to measure their heart rate
independent practice T:After a significant number of students have demonstrated their ability