These three companies just didn't live up to Mr. Market's expectations last week. Sometimes an earnings stumble is a signal to sell, but digging in the dirt is also a good way to find turnaround candidates while they're getting beaten down.

Today, you'll see just how much disappointment we can find, even between those hectic earnings seasons.

High-end hopes
Broad-line chip designer National Semiconductor  (NYSE:NSM) opens this week's ceremonies with a very slight earnings miss. Analysts had hoped for net profits of $0.34 per share on $469 million in revenue, but had to settle for a penny less and slightly lower sales. Both numbers were on the lower end of management guidance.

It was a plain old miss on the top line, as sales fell a bit from year-ago levels. But even though net income fell 7% from last year, a generous share buyback program actually boosted earnings per share by 10%.

National's hopes for the future lean heavily on high-margin analog processors and a promising foray into solar cell technologies. One-third of the company's current sales still derive from the cell phone market. National chips power important parts of Apple's  (NASDAQ:AAPL) iPhone and many of Research In Motion's  (NASDAQ:RIMM) BlackBerry smartphones. As long as there's demand for highly capable handsets like those, National won't need to do anything silly like transforming into a pure solar-power business.

The revenue stream may not be growing, but thanks to that lucrative product mix and plenty of free cash flow to spend on share buybacks, the bottom line has a lot of growth left in it. The stock is trading near six-month lows, at only 15 times trailing earnings -- a historically cheap valuation for this semiconductor veteran. This one belongs on your research list, Fool.

New losses on the block
This far away from the tax report deadlines, we rightly expect very little out of H&R Block (NYSE:HRB). Underperforming rock-bottom expectations like that is quite a feat, but Block pulled it off with flair and gusto.

A $0.40 net loss per share from continuing operations fell far short of Wall Street's more optimistic outlook of a $0.35 per-share loss. Revenue dropped 11% from year-ago levels, although the company narrowed last year's loss of $0.93 per share.

Wall Street analysts still love this stock, with four "buy" ratings and two holds against one "underperform" and no sell recommendations. But we're playing a different tune in our Motley Fool CAPS investor community, where only 47% of the players with an opinion point a thumb skyward. Our players cite a litany of problems, including crazy valuation, a lack of management transparency, a weak balance sheet, and increasing competition in the core tax-preparation market.

This report did little to mollify any of those concerns. The company is getting out of the mortgage-lending business as fast as humanly possible, and it's buying some of its own franchisees to bump up its sales and profits a bit. While those moves are welcome, I'm not sure they're enough to sustain the share price at close to three-year highs for very long.

Come next tax season, I think Intuit  (NASDAQ:INTU) will steal another chunk of market share in the sector. H&R Block pulled in $2.4 billion of sales from tax services in fiscal 2005, and $3 billion last year. Intuit grew its tax sales from $836 million to $1.25 billion in the same time frame. Over three years, that's 8% annualized growth for H&R Block, versus 14% for Intuit. I suspect that trend will continue until online tax preparation goes out of style.

Monitor this one
Let's end on a happy note, folks. Chinese medical-device maker Mindray Medical (NYSE:MR) doubled its quarterly sales to $146 million in last week's report, and tacked on another 17% to GAAP net earnings, bringing in $0.21 per share. That cocktail fell a slim penny short of analysts' average earnings estimate.

Think of Mindray as a smaller, Cantonese-speaking clone of Abbott Labs (NYSE:ABT). Mindray specializes in patient-monitoring systems and diagnostic tools, and it's growing rapidly in the global market. The local Chinese market provides plenty of growth, of course, but there's a big world beyond the Great Wall, too. Mindray's efforts to get its devices cleared for use in Europe, the U.S., and elsewhere show a lot of business sense.

This is both a five-star CAPS stock and an official Motley Fool Rule Breakers recommendation. You can't lose anything by learning more about this explosive growth engine.

Signing off
Some of these underperformers are victims of larger circumstances, while others might have only themselves to blame. It's up to you to decide which down-on-their-luck companies should be able to pull themselves up by the bootstraps, and which ones are stuck in the mud for real.

Further Foolishness:

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Mindray Medical is a Rule Breakers pick. Apple is a Motley Fool Stock Advisor recommendation. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Anders Bylund holds no position in the companies discussed this week. See his current holdings for yourself. The Fool has an ironclad disclosure policy.