Hi Chris! I'm assuming that when you say elementary students, you mean those at that linguistic level (i.e. teenagers ~ adults) rather than age per se (but if you actually mean schoolkids aged from about 4-10, then in my experience they don't ask questions, at least not (m)any about linguistic form!). If so, everything and anything can be a problem (certainly, if not taught very well), but again, the students in my experience don't so much ask questions (at least, not at all probing ones, and this time that is to do with their inability to form and ask at all sophisticated questions about much, let alone grammar, rather than due to age/lack of cognitive development and awareness per se like it is with elementary schoolchildren) as simply exhibit inability or incomprehension in performing activities and tasks.
So I'd hazard that there are more questions to be had from students who are more going on intermediate, and who thus have not only greater linguistic ability but also more experience of English and thus chances to be puzzled about something or other.
All that being said however, if you post this on the Applied Linguistics or Adult Education forum you might get differing responses to mine here.
