A study investigated whether children and adolescents use commas and the principle of Late Closure to guide sentence parsing decisions as adults do in processing syntactically ambiguous sentences. The study consisted of three experiments, conducted similarly but with different subject groups: 24 university students; 24 fourth-graders; and 19 sixth-graders. In each, subjects read sentences containing different arrangements of pre-posed and main clauses and comma use, and answered simple comprehension questions, all presented on a computer using a self-paced, one-word moving-window procedure. Results indicate that all groups had shorter reading times on the main clause verb in late closure sentences than in early closure sentences, supporting the domination of late closure parsing strategy. While results for adults supported the predicted patterns of comprehension speed involving closure and comma, they were not statistically significant. The fourth-graders appeared not to use information about the comma to override the late closure parsing strategy. The sixth-graders were clearly sensitive to the late closure strategy, but did not use comma information as effectively as did adults. Reading times were similar to those of fourth-graders. Four figures and one table support the data. (MSE)