comScore has released its Media Metrix rankings for the top 50 web properties in the U.S. in September.

“Students and teachers were back in the classroom in September, resulting in a surge in traffic to Education sites that earned it the #1 spot on the top-gaining categories chart,” said notes Jeff Hackett, executive vice president of comScore. “September also marked the first time that popular social media site Pinterest cracked comScore’s Top 50 Properties ranking as it surpassed 25 million visitors for the month.”

Google Sites, while still at the top, remained flat from month to month at 187 million visitors. Microsoft Sites took second place again at 167 million, down from 170 million the previous month. Yahoo Sites took third place again with 164 million, which is the same as it had the previous month.