MANCHESTER — Superintendent of Schools Thomas Brennan painted a dire picture of the Manchester School District under the mayor’s proposed school budget, at one point pausing to compose himself during a difficult question-and-answer session Tuesday night.

If $12 million in proposed reductions are enacted, Brennan told aldermen that class sizes will swell to more than 30 students, and that advances the district has made in reading, writing and math standardized test scores could be lost. Principal and assistant principal layoffs could affect student safety, Brennan said.