<p>I knew a kid that learned pre-cal over the summer and then took Calc AB. He did extremely well. </p>
<p>Taking pre-cal and calc BC at the same time is silly and defeats the purpose. It is called "pre"-cal because it's supposed to be taken before calc! You might be able to take Calc AB, but Calc BC will be really, really tough. If you're really good in math, it might be doable. </p>
<p>There aren't really topics in pre-cal that won't be gone over again, but pre-cal kind of lays a foundation for further math.</p>