The S&P 500 (SNPINDEX:^GSPC) roared back from its poor performance during the summer, climbing more than 8% to finish the month of October at 2,079. Yet within the S&P 500, some stocks had a greater influence on the index's gains than others. In particular, SanDisk (NASDAQ:SNDK), KLA-Tencor (NASDAQ:KLAC), and TripAdvisor (NASDAQ:TRIP) were among the S&P 500 components that had the most upward pressure on the index.

In the following slideshow, you'll learn more about why these three stocks rose so much this month. By watching when the stocks in your portfolio make big moves, you can gather the information you'll need to make smarter decisions about how to respond, and that will help make sure that you don't make mistakes either from doing nothing or by doing the wrong thing.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool owns shares of and recommends TripAdvisor. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.