I actually don’t think there’s a strong correlation with ACT math and mathematically ability at higher levels. While it is still a positive correlation, its doesn’t tell the whole story. ACT math isn’t difficult, its mostly about speed. ACT math is like a 100 m race, versus 10km at Calculus and above. I’ve met a few people in Tau Beta Pi who only had a 29 or 30 composite ACT score.