Investors interested in Schools stocks are likely familiar with K12 (LRN) and Afya (AFYA). But which of these two companies is the best option for those looking for undervalued stocks? Let's take a closer look.There are plenty of strategies for discovering value stocks, but we have found that pairing a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system produces the best returns. The Zacks Rank is a proven strategy that targets companies with positive earnings estimate revision trends, while our Style Scores work to grade companies based on specific traits.Currently, K12 has a Zacks Rank of #1 (Strong Buy), while Afya has a Zacks Rank of #5 (Strong Sell). This system places an emphasis on companies that have seen positive earnings estimate revisions, so investors should feel comfortable knowing that LRN is likely seeing its earnings outlook improve to a greater extent. However, value investors will care about much more than just this.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their current share price levels.Our Value category grades stocks based on a number of key metrics, including the tried-and-true P/E ratio, the P/S ratio, earnings yield, and cash flow per share, as well as a variety of other fundamentals that value investors frequently use.LRN currently has a forward P/E ratio of 17.29, while AFYA has a forward P/E of 23.99. We also note that LRN has a PEG ratio of 0.86. This figure is similar to the commonly-used P/E ratio, with the PEG ratio also factoring in a company's expected earnings growth rate. AFYA currently has a PEG ratio of 0.97.Another notable valuation metric for LRN is its P/B ratio of 1.81. The P/B is a method of comparing a stock's market value to its book value, which is defined as total assets minus total liabilities. By comparison, AFYA has a P/B of 3.48.These metrics, and several others, help LRN earn a Value grade of A, while AFYA has been given a Value grade of D.LRN has seen stronger estimate revision activity and sports more attractive valuation metrics than AFYA, so it seems like value investors will conclude that LRN is the superior option right now. 5 Stocks Set to Double Each was handpicked by a Zacks expert as the #1 favorite stock to gain +100% or more in 2021. Previous recommendations have soared +143.0%, +175.9%, +498.3% and +673.0%. Most of the stocks in this report are flying under Wall Street radar, which provides a great opportunity to get in on the ground floor.Today, See These 5 Potential Home Runs >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Stride, Inc. (LRN): Free Stock Analysis Report Afya Limited (AFYA): Free Stock Analysis Report To read this article on Zacks.com click here.