A total of 271 early childhood professionals completed pre- and post training knowledge assessments in True-False only (TF) or True-False with "unsure" option formats (TFU). In Study 1, only TFU format was used. In Study 2, participants were randomly assigned to TF or TFU formats. Responses which were initially "unsure" were more likely than confident responses to become "correct" at post test. Hence, teachable moments may be created when individuals acknowledge being unsure, and adding "unsure" to these tests may help identify such moments. The TFU format, in addition, better captured participants' gains in knowledge, and helped identify three types of responses: confidently correct (correct at pretest and post test), confidently incorrect (incorrect at pretest and post test), and unsure-then-correct. The latter two responses may help target instructions. In sum, adding an "unsure" option may improve sensitivity of tests, and inform continuous quality improvement of early childhood professional development trainings. (Contains 3 tables and 1 figure.)