The use of grid-in formats, such as those requiring students to solve problems and fill in bubbles, is common on large-scale standardized assessments, but little is known about the use of this format with a more general population of students than high school students taking college entrance examinations, including those attending public schools in grades 8 and 12. Data were taken from the National Assessment of Educational Progress (NAEP) mathematics field test for 2,673 examinees in grade 8 and 2,793 in grade 12. It was expected that there would be effects from requiring the grid-in format, especially for items that were regularly multiple choice, but the effects of the grid-in format are larger than expected for short constructed response items. Students were also inconsistent in what they wrote in the blocks and what they gridded below the blocks, resulting in a correct response in one format and not in the other. The presence of the grid-in response format items apparently discouraged some students from attempting items, and this effect seems to extend through the blocks containing the grid-in items to other items. The results indicate that substantial student practice and familiarity with the format will be a necessary condition to the use of such items. (Contains 12 tables.) (SLD)