In a common pattern of the last few years, the American economy, after a dismal start to 2015, regained its footing in the spring and looked set to continue a modest advance for the rest of the year.

But the lackluster data last quarter and a slight downward revision of the estimated growth rate over the last three years underscored the challenges that still lie ahead for an economy that doesn’t seem to be able to move ahead at more than a slow jog.

The rebound in April, May and June was largely expected, but the 2.3 percent annualized rate, adjusted for inflation, that the Commerce Department reported on Thursday in its initial estimate was a bit below what economists on Wall Street predicted before the release.

Investors were not impressed, and major stock market averages moved little.

“I think it’s an O.K. performance,” said Nariman Behravesh, chief economist at IHS, a research firm based in Lexington, Mass. “Underlying growth is stable but not spectacular. The economy is plodding along.”