If I put enough time (& money) into my step son, will he experience sharp improvements?

Many students for whom a four-year engineering track may appear too math-intensive, turn to engineering technology programs, which include two-year programs with a more hands-on focus:

http://www.abet.org/accreditation/new-to-accreditation/engineering-vs-engineering-technology/

Perhaps this might be a more attainable goal with real payoffs. You can search the ABET site for programs, including in your area, that might be a good fit for your stepson: http://main.abet.org/aps/Accreditedprogramsearch.aspx.