The Stock Market Is Offering a Once-in-a-Generation Investment Opportunity. Here's How You Can Participate.

All signs point to this market trend reversing in the near future.

The last decade has been very good for stock investors. The S&P 500 ( ^GSPC 0.32% ) has produced a total return of more than 300% since September 2015. The tech-heavy Nasdaq Composite index ( ^IXIC 0.25% ) has climbed even higher, with a total return exceeding 400% in that time.

But not all stocks have participated equally in that rally. The biggest companies have grown bigger while smaller stocks get left behind. That's seen not only in the record-high concentration of the S&P 500, but in the lagging performance of small- and mid-cap stocks. Small-cap stock indexes like the Russell 2000 and S&P 600 are up just 142% and 155%, respectively, in the same period.

But that may have created a once-in-a-generati