After lagging in the first five months of 2017, small cap stocks have regained their sheen and outperformed the broader U.S. market in June. This is especially true as the ultra-popular small-cap ETF (IWM – Free Report) is up 3.5% this month compared with a gain of 1.1% for the mid-cap counterpart (IJH – Free Report) and flat return for the large-cap cousin (SPY – Free Report) .