Feeling that “some prep is necessary” does not necessarily mean that one thinks that any particular test-prep cram school (or type of such school) is a good value for the time and money. Indeed, I don’t see why the high value preparation (test familiarization and such) is difficult to do in a relatively short time at home or in the library. But doing hundreds of SAT(-like) questions or memorizing thousands of supposed SAT words seems like a low value proposition; the kid’s time would likely better be spent doing other academic, intellectual, athletic, and/or artistic activities.
Is that really “one of the best public magnet high schools in the country”? (Of course, a common criticism of IB programs is the very high volume workload compared to the content matter learned – one can argue that IB programs are also not exactly high value in terms of learning for the amount of time spent.)