Engineering does not require that good math. More important is how to use the math. I had less than 70 in math back to early 80 in Chinese College Exam and went to a regular local college in China.
I have been designing EE equipments near 20 years in US, competing MIT-graduates neck to neck.
I hired few recent graduate-EE. All had SAT less than 1800 and went to local State Engineering Scchools. Both handle their jobs well.
If your son 感觉学工程也能对付, I am sure he will be fine in Enginering field.
