BOSTON - Most toddlers with frequent ear infections don't need ear tubes to preserve normal learning and behavior through primary school, according to a study challenging one big reason for these common procedures.

Repeated ear infections - even some colds - can leave a fluid buildup that specialists long feared would dampen hearing and slow language and other learning. However, it now appears the hearing loss is too short-lived and mild to interfere with learning, at least in the vast majority of children.

"Children are basically pretty resilient and can withstand ... that little amount of problem," said study leader Dr. Jack L. Paradise, a pediatrician at the University of Pittsburgh.

This was first shown true at age 3 by the same team of Pittsburgh-based researchers in 2001. Their later research found the same thing true into early school age. In 2004, professional groups eased the guidelines that had long dictated quick surgery to clear accumulated fluid.

The Pittsburgh group now makes the identical finding for ages 9-11 in a government-funded study of 391 children. The work was being published Thursday in the New England Journal of Medicine.

"People were always worried: Are there late effects?" said Dr. Stephen Berman, a University of Colorado pediatrician who wrote an accompanying editorial. He said this study is "very, very reassuring" that there aren't.

The children in the study were tested for skills in hearing sounds, reading, writing, socializing, conduct and intelligence. Children who got ear tubes quickly did no better than those who waited up to nine months to check if the fluid remained - and only then got implants if needed.

The plastic tubes - with a diameter the size of a pencil lead - are implanted in the eardrum to ventilate the middle ear, cut down on future fluid, and drain it when infections develop. The surgery has small risks, including those of general anesthesia and possible hearing loss from damage to the eardrum. Ear tubes generally fall out after a year or so.

There are no reliable current estimates on how many ear tubes are implanted each year. About 550,000 were placed in 1996 - about half in toddlers. It has been the No. 2 surgery in the nation, after circumcision. Today, the surgery can cost $3,000 or more.

Berman believes tens of thousands of surgeries could now be considered unnecessary each year. However, a minority of children with severe hearing loss will remain candidates for the surgery. Also, many tubes are implanted to cut down on the infections themselves, rather than fluid. They can reduce pain, and that justification remains valid.

The study was backed by the National Institute of Child Health and Human Development, the Agency for Healthcare Research and Quality, and drug makers GlaxoSmithKline and Pfizer.