Assessment for learning is a natural extension of those lessons you learned in the sandbox. We learn through experience, experimentation and error. Despite this, schools have traditionally used summative assessment, which serves to freeze the moment. This ices experimentation as a punishable mistake and robs error's ability to provide life's "sandbox" lessons.
Assessment for learning frees up the learner to play and learn in a natural union as they did when they were children. Learning is less threatening, less limiting: exploratory. Formative assessment celebrates the mistake and encourages growth.
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"Experience is not what happens to you. It's what you do with what happens to you." Alduous Huxley