Self-evaluation for students is today a widely recognized practice, and it is strongly related to increasing meta-cognition and to enable students think critically. Most commonly used term attached to students' self-evaluation is rubrics. Very many rubrics helpers can be found online, but then again the very idea of using them is ruined. Effective use of rubrics and other self-evaluation tools is implemented in the teacher's planning process and tightly bound to the learning goals and desired learning outcomes, because then and only then it will enable the meaningful and successful deep learning.
Self-evaluation should be started as soon as possible, because it allows your students create realistic self-images as learners. Knowing what one can do, and what is challenging really helps students target their learning efforts to the right spot. Too much valuable time and energy is wasted in schools when learning is not targeted well. Self-evaluation helps to target it right. It also gives extremely valuable information for the teacher.
The first self-evaluation practices should be really easy: just include to the assignments a line or two where students get to tell if the task was too easy or too hard. Also add a row of smileys. Students should circle the correct face (smiling, unsure, unhappy) to indicate how well they think they performed the assignment. These students' self-evaluations are also very helpful while discussing with parents, because they show more of the learner's own thinking, and thus can be used as tools to teach more meta-cognitive skills (hopefully with parents help).
To effective self-evaluation applies the same set of rules as to all teaching: it must be safe, transparent and consistent. Good and reciprocal interaction between students' self-evaluation and your feedback of their learning creates the best possible frames for autonomous, deep, meaningful learning. May I help you create that to your classroom?