Hi! For writing, in terms of productive vocabulary, you could try using the Vocabulary Knowledge Scale by Paribakht and Wesche. The productive segment covers sentence writing, and the test can be modified to suit your research needs. Worth a look. All the best!
For reading: Select different texts such as simple, and complex paragraphs from news papers, story books etc.
Writing : essay writing selecting different topics with a limited number of words is suitable. And, prepare a questionnaire to test grammar, vocabulary etc.
In my opinion,you should determine the toipcs of the writing skill that you wanna them to write such as argumentative or disscussion, if you want good results in writing.Next, start by exposing your learners to these planned topics by using skimming,scanning,previewing,and guessing.Train them for some classes to get answers and give them extra drills.Then, guide them in writing and you can exercise them on the writing various genre.