This study aimed to develop a two-tiers diagnostic test to assess the high school, junior high school, and elementary pre-service teachers about the heat and the temperature concepts in a general physics course. There are two tiers in this test: The first tier composed of six items consisting of multiple-choice questions related to the heat and the temperature, including the correct answer. The second tier of each item contains reasons for students choosing their answer to the first tier. The second tier included four or five responses, one of which is a correct conceptual understanding. The wrong answers, also called distractors, were based on students’ misconceptions. To this end, 128 pre-service teachers from Quebec in Canada completed a pencil-paper questionnaire of sixty minutes duration composing of six questions (four open-ended questions and two multiple choice questions with justifications). As illustrations, the following  conceptual understandings have been identified in our qualitative analysis of the data collected: 1. The change of state of the matter does not require a constant temperature; 2.  The temperature is a measure in degrees to indicate the level of heat of an object or person; 3. The mercury contained in a thermometer expands when it is heated so that the particles which constitute it expand; and 4. The sensation of cold (or warm) is related to the difference in temperature.