Allowing students to re-attempt assessments has been shown to be effective in traditional university-level courses in improving student mastery of course content. In this paper, we analyse an intensive programming introductory experience, where first semester university students’ full load is a single semester-long course that teaches the basics of programming and software engineering. We study its use of mastery-based grading: offering five (formative) low-stakes quizzes (with retakes), each focused on a single topic, and five (summative) higher-stakes exams that assess all learning objectives. Our research questions are: (i) "Do second chances help students to increase their performance over time in intensive courses?‘‘; and (ii) ``Are second chances effective in reducing stress/mental load/weight of assessments in intensive courses?’’. We find that (i) offering second chances on quizzes decreases the number of students at risk of failing before the first exam; (ii) students’ proficiency in coding tasks (as measured by exam grades) improve during the semester; and (iii) that our schedule reduces anxiety and mental load for students, but only after students take the first chance.