The following forum has a thread for precalculus questions, but for your son might want to remark that he is 9, when posting, so they don't get smart alecky over an elementary question. I'm not saying they will, but that is younger than the average poster. http://www.physicsforums.com/forumdisplay.php?f=152 or just start up a thread here for questions and some of us teachers could chime in. (What does "just visiting" mean? few posts? wrong shoes?)

Hi. I would place him/her right in the same pleasant world I inhabit myself, enjoying the beauty of math. Is that what you meant? On my page at UGA: http://www.math.uga.edu/~roy/ that file I linked was only days 1-5 of a 30 day course which will almost certainly go well past what your 9 year old has seen. Day 14 is already past what I found in the AOPS intro to number theory book. Ask your son to find which prime numbers up to 100 are expressible as the sum of two squares. E.g. 5 = 1^2 + 2^2, but 7 is not. Then have him make a guess as to what the ones have in common that are. i will remark that as a professional mathematician my impression is that there is a whole world of free materials out there, and that gifted parents are to some extent taken advantage of by being sold expensive books targeted at them. Lots of gifted kids can read real books just targeted at bright learners. My webpage has a lot of free sources, mostly high level of course, but some not all that high. Those epsilon camp geometry notes on there were used with 8-10 year olds last summer quite successfully I think. Here is link to a free number theory book. It states a lot of high level prerecquisites but they are not visible in the first chapter at least. http://wstein.org/ent/ here is a free link to the best algebra book i know of, by euler: http://archive.org/details/elementsalgebra00lagrgoog David Henderson has a nice geometry book that tries to teach ideas by guided problem solving. It costs over $60 new on Amazon, but here is a used one for less than $10. http://www.abebooks.com/servlet/SearchResults?an=david+henderson&sts=t&tn=geometry&x=61&y=7

Here is a geometry book written by a world famous geometer for his son's 8th grade class. the used copies are under $5. Some sections use a little trig. http://www.amazon.com/gp/offer-listing/0387975640/ref=sr_1_fkmr2_2_olp?s=books&ie=UTF8&qid=1339095037&sr=1-2-fkmr2&condition=used my "epsilon camp notes" , were taught to 8-10 year olds as a guide to reading Euclid. at least they are free. no trig is used, indeed the geometry is used to motivate both algebra and trig (as was the case historically). http://www.math.uga.edu/~roy/camp2011/10.pdf

This may seem nuts, since these notes were written for my college students, but I have found that with guidance, bright children can do math that was aimed at average college students. At least they are free. These notes discuss integers, prime numbers, and gcd's. http://www.math.uga.edu/%7Eroy/4000.01-05.pdf

I am just learning to post and this my second try at this remark.. We were part of a program where a student was learning to give IQ tests, so for us it was free. This was at the UGA Torrance gifted education center in Athens GA, long ago.

Here is one that costs $1000 for 8 weeks of online camp, but they said they had lots of scholarship money available this summer. http://euclidlab.org/programs/camp-euclid/program-description

" IQ testing was way too costly for us, and our homeschooling was going well without it. " I am a new member and one of last summer's geometry professors from epsilon camp. Just a comment on testing cost. When our kids were young, we had them tested for free at the University of Georgia gifted center, where Paul Torrance was director. Maybe they needed subjects and made a special exception, but it worked for us. I especially enjoyed meeting Paul Torrance. He was very inspiring and encouraging. His books on giftedness helped us as well.