If he wants to go into engineering he should be taking a closer look at STEM universities and not just the Ivies. With the exception of Cornell, Ivies are lacking in depth of offerings in many engineering fields. EG: compare Harvard to MIT.
Really strong engineering programs actually are scattered all over the US. Look at Universities like Rice, Cal Tech, MIT, Case Western, RPI, WPI, Stevens, CMU, Purdue, Illinois, VPI, TX A&M, Colorado School of Mines, Stanford (not an Ivy), Harvey Mudd, Georgia Tech, Rose Hulman and Olin, et al. Check out engineering programs at your state university. Their offerings often exceed most Ivy offerings in engineering. All of the engineering students in the programs listed above are virtually straight A students and job/graduate school options are not an issue. Engineering/science industries know who they are.
In any case, he wants the best math, physics and chemistry courses he can find in his high school. He wants A’s in most everything. The minimal math required for engineering applicants is pre-calculus, AP math is not a requirement. The most important math course may well be the second year of algebra… learn it well! Most of these universities will require AP test scores of 4 out of 5 or better before these secondary school courses will actually be accepted for college credit.
What grade is he entering?
When/if possible it would be helpful to take a summer research program at the local university. If income qualified, some of these programs are available in urban areas to local students at little or no costs. If they exist in your area, your secondary school science /math departments should know about them.