Research has shown that differences in the prior knowledge of the participants and in the learning indexes adopted can explain why some studies show positive learning effects of analogy enriched text while others do not. In the present studies, these two factors were combined into one through the construction of a learning index that measured incremental positive changes in the participants' prior knowledge after reading an analogy enriched or no analogy text. A second learning index was also used to evaluate whether the participants created well-formed conceptual models after reading the science text. These learning indexes were used in two studies in which the effects of analogy enriched versus no analogy text were compared on the learning of the scientific explanations of the day/night cycle and of the seasons. The participants were 3rd and 5th graders in the first study and 6th graders and college students in the other. Although only few of the participants learned the correct scientific explanation, those who read the analogy enriched text produced more incremental positive changes in their pretest explanations at posttest and delayed test and created more well-formed conceptual models close to the scientific one than those who read the no analogy text. They also recalled more information and created fewer invalid inferences in their recalls. The results indicate that analogies can be used without reservation to facilitate the learning of science and have broader implications about how to evaluate the learning of science in general.