It feels as if summer vacation has barely started and the back-to-school ads are already showing up in flyers and on television. As you rush to meet the needs of your kids—buying everything from pencils and paper to smartphones and laptops—plenty of stock-market pundits are touting something else: back-to-school stocks.

For years, investing in those kinds of stocks seemed like a wise idea. The shopping season filled the nation’s retailers with optimism and excitement because it was second only to the end-of-year holiday period for total retail activity. So investors and analysts kept a close eye on the stocks that would benefit—companies such as Apple (AAPL), Staples (SPLS), and Gap (GPS). That’s because they gave important clues about the willingness of consumers to spend—and pay for brand names—and how likely they were to wait until the last minute to get deals on sales.

Be sure to also read "Your Guide to Back-to-School Shopping."

Investing in seasonal stocks, though, is never a good idea. That’s particularly true for back-to-school stocks. One reason: Investors who try to time the market are usually disappointed. It’s far too risky, and most individuals don’t know more about those stocks than the broader market. A better approach, in our view, is to dollar cost average purchasing shares of stocks over a longer period of time.

Another reason to be wary is that consumers don’t spend the way they did before the Great Recession. In recent years, to entice them to spend more, some retailers have been offering bigger than usual discounts on their products, which makes it harder for investors to forecast retailer margins and profits. Last year, for example, total back-to-school spending declined to $26.5 billion from $30.3 billion just two years earlier, according to the National Retail Federation. With consumer spending stuck in a funk, it won’t be a surprise to see another disappointing back-to-school season for retailers.

Why aren’t consumers spending more? A combination of economics and attitudes are to blame. True, the labor market is much improved, but wage growth has barely budged. At the same time, consumers have become more sober custodians of their discretionary dollars. By some estimates, the decline in gas prices was supposed to boost consumer spending by $70 billion over the past year. Of course, that didn’t happen. Rather than spending the gas windfall at a mall or big-box store, the average American chose an alternative: to save or pay down debt.

As a result, it’s been hard to find any back-to-school stocks that have consistently exceeded analysts’ earnings and revenue estimates in the past couple of years. Old back-to-school stalwarts like Wal-Mart (WMT) and Target (TGT) are suffering from stagnant sales. Some of the mall-based teen retailers such as Abercrombie & Fitch and Wet Seal are struggling to survive. Shares in retailers like Macy’s (ticker:ticker::M) and the Gap (GPS) have barely remained in positive territory for much of the year. In many cases, bets on individual retail names have either been money losers or they have failed to match the performance of the broader market.

The Dynamic Retail exchange-traded fund (PMR), has also suffered. The ETF is heavily weighted toward typical back-to-school names like Walgreen Boots Alliance (WBA), Costco (COST), and Kohl’s (KSS), and it has trailed other retail ETFs and the broader market, falling almost 1 percent since the beginning of the year.

By comparison, more diversified ETFs have fared better. The SPDR S&P Retail ETF (XRT), for example, includes non-back-to-school stocks such as Netflix (NFLX), Rent-a-Center (RCII), and the Asbury Automotive Group (ABG). Since the beginning of the year, it has gained almost 2.5 percent. The same goes for the Market Vectors Retail ETF, which is heavily exposed to Home Depot (HD) and Lowe’s (LOW) and has risen 5.5 percent so far this year.

The bottom line is that relentless macroeconomic headwinds make investing in so called back-to-school stocks a risky prospect. Our advice: When the back-to-school ads start showing up on TV, the radio, and the Internet, invest your money in binders, backpacks, and calculators (and smartphones and smartwatches, if necessary). But don’t risk investing in the hopes of profiting from the back-to-school season. It very likely won’t happen. $

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