I have completed 7 terms in UCMAS. Due to my shifting to new place i was unable to complete the graduation in it. So I guess I can answer it due to my experience. Pros we all know that increases your speed and efficiency in calculation. It does improves the concentration. But some of its cons are actually for younger kids. Especially of smaller classes as they just complete their calculations through tricks used in UCMAS. So they use same things in their school level papers and just solve questions without solving it by proper methods and this affects their grades in school.