NEW YORK ( Insider Monkey) - For the past seven weeks, Insider Monkey has been publishing articles about the stocks insiders were buying like crazy. The stocks we listed in the previous six articles have performed spectacularly compared to the S&P 500. Insiders know more about their companies than do most investors. This holds especially true in smaller companies, which are either followed by only a few analysts or none at all. Academic studies conducted during the past 40 years confirm that stocks bought by several insiders outperform the market by about 7 percentage points per year in those studies. Last week, we brought three more companies insiders are buying to your attention. Here are their performance numbers since we highlighted them: No. 1: Trailer Bridge ( TRBR). Trailer Bridge was also in our list during the previous week, returning 19% vs. 1.7% for the S&P 500 index. Last week TRBR returned another 6% whereas the S&P 500 index lost 0.7%. No. 2. Ladenburg Thalmann Financial Services ( LTS). Ladenburg Thalmann has been the worst performer among dozens of stocks we selected. LTS lost 10.1%, underperforming the SPDR S&P 500 ETF ( SPY) SPY by 9.4 percentage points. No. 3. Career Education ( CECO). Career Education Corp has been satisfying our criteria over the past couple of months and we talked about it several times. In November and early December insiders were buying CECO shares at around $18. The stock closed at $21.57 on Friday. Steve Eisman's Frontpoint Partners has been shorting for-profit education companies whereas Richard Blum is long CECO. Last week, CECO increased another 1.6%, beating the SPY by another 2.3 percentage points. Overall, two out of three stocks we picked managed to beat the market. Unfortunately the average return of this portfolio was -0.8% vs. -0.7% for the S&P 500. This is the first time in seven weeks our selections underperformed the SPY. Here are three stocks insiders were buying like crazy last week: No. 1. A. Schulman ( SHLM). Barrington's James Mitarotonda has been buying more than 15,000 shares during the past few days. In his last transaction he paid $21.35, which was also the closing price for the stock on Friday. Schulman's Chief Marketing Officer Paul R. Boulier purchased 1,200 shares at $21.08 a few days earlier.