Design your on and off the job assessments carefully. Integration happens before the actual job assessments are conducted. This is because you need to structure the assessments to have as much in common as possible. See if there are common questions. If you want to use grades or numbers alongside comments, then design a common grading system. See if the assessments can be broken down into common subsections. For example:
Training needs.
Selection procedure.
Time.
Effectiveness of training.
Performance.
Student response.
Goals and objectives.
Take into account the aspects of both assessments that are not compatible. The general theory is that the longer the course, and the more complex the course, the less likely it is you will be able to seamlessly integrate both assessments.
Gather your data from the on and off the job assessments. Compile the data for each assessment as you would normally. In the end, you will have aggregated data for on the job assessments (practical) and off the job assessments (theoretical).
Use your aggregated data to form an integrated assessment. This is best done where there are common features between the on the job and off the job assessments. Compare and contrast these. Create separate sections within the combined assessment for aspects of the practical (on the job) and theoretical (off the job).
Examine how the theory learned in class (off the job assessment) is put into practice in the workplace (on the job). This form of integration ties the strands of both on and off the job assessments together. If there are a number of non-connecting strands, then there may be a problem between the two. For example, if a plumber repairs water heaters, but water heater repair is not covered in class, then the student will be at a disadvantage.
Learn from each on and off the job assessment. By doing this, you will learn to better integrate the two in the future. If the two assessments appear extremely difficult to integrate, ask yourself if it is worth it. If you feel it is, then you should re-examine the overall course structure. The easiest way to do this is to bring the off the job studies more in line with the practical. This usually means reducing the amount of abstract theory.