Also, the more time that children spent in child care, the more likely their sixth grade teachers were to report problem behavior.
The findings come from the largest study of child care and development conducted in the United States. The 1,364 children in the analysis had been tracked since birth as part of a study by the National Institutes of Health.
In the study's latest installment, being released Monday, researchers evaluated whether characteristics observed between kindergarten and third grade — generally ages 5 to 9 — were still present in fifth grade or sixth grade, when children are around ages 10-12.
The researchers found that the vocabulary and behavior patterns did continue, though many other characteristics did dissipate.
The researchers said the increase in vocabulary and problem behaviors was small, and that parenting quality was a much more important predictor of child development.
In the study, child care was defined as care by anyone other than the child's mother who was regularly scheduled for at least 10 hours per week.
The researchers said the enduring effect of child care quality is consistent with other evidence showing that children's early experiences matter to their language development.
The long-term effect on behavior also may have a logical explanation, the researchers said.
"One possible reason why relations between center care and problem behavior may endure is that primary school teachers lack the training as well as the time to address behavior problems, given their primary focus on academics," the researchers said.
The study appears in the current issue of Child Development. The authors emphasized that the children's behavior was within a normal range and that it would be impossible to go into a classroom, and with no additional information, pick out those who had been in child care.
By Kevin Freking