This article presents research designed along one scholar course with first-year pre-schoolers in Spain. A coherent sequence of learning activities, that combined classroom work with working outside the classroom (in the school garden), was designed in order to analyse if the first-year-preschool children were able to apply scientific tools, including the magnifying glass and dichotomous key to observe, compare, classify and identify small animals within their surroundings. The results obtained show that using a magnifying glass, pupils learned to observe in an intentional way to, by means of counting the number of wings and legs and the colour of small animals, compare small animals. The comparison criteria they established based on this observation and comparison, were used to classify and identify other animals by using a dichotomous key. The results show that the students struggled to use keys; thus, help from the teacher was necessary to develop scientific skills as observe, compare, classify and identify.