Mindfulness is the quality of being conscious and aware of the present moment harmonizing mind and body. This study presents a six-week intervention program carried out in four educational establishments in Granada with 5th and 6th grade primary school students and 1st, 2nd and 3rd year secondary school students. The aim was to find out whether Mindfulness has positive effects in terms of improving students’ attention and reducing stress. The samples were 320 students; a quasi-experimental design was used. We collected socio-demographic and family data and carried out a pre-test to measure the attention variable by means of the d2 questionnaire and the stress variable with the Inventory Questionnaire of Childhood Stress. Following the intervention, we carried out a post-test using the same instruments. A mixed linear model was used to study the effects of the Mindfulness program. The results show that applying a Mindfulness program improves attention and reduces stress in these students, with differences by sex, school- and ages.