K.P.
It's wonderful that you are son involved in your boyfriend's family. The more caring adults the better... but this isn't really up to you!
Honestly, if he's 14 and bombing out in school, then he needs to try something. You can ask to see the doctor's report and suggest that he be evaluated by a psychologist if that hasn't already been done.
It is actually a misconception that ADHD kids are "poorly behaved and always off-task". If something is interesting to them, they can focus for extended periods of time (like video games, movies, sports). If an activity is highly cognitive or not of high interest, they cannot remain on-task. ADHD is probably the most inaccurate name in recent history (this coming from the man who coined the term) b/c in actuality, people with ADHD attend to EVERYTHING and cannot just focus on what is relevant. They are easily distracted and tangential.
Concerta is a relatively safe medication and 30 mg (depending on his weight) is appropriate for a child his age. Medications are traditionally prescribed if the condition is significantly impacting the child's daily life. It should not be applied without behavioral therapy and should be regularly monitored by a physician (bloodwork).
Don't rule it out b/c you are against it. Unless this is your area of study, then you really only know what you can read about the condition... it is far more complicated than implied on the internet or in parenting magazines.
I posed this question last week to a similar query, but cannot take credit for it. This was a question posed at a psychiatric conference I attended several years ago... "If we were talking about a child with diabetes would you deny the use of insulin? Yes, you would modify his diet and his exercise, but you you would not hesitate to supplement with a chemical.". This is no different.