Growth measures from where the student started to where they are now. For instance, if a student begins third grading reading 75 words per minute at a 70% accuracy, and ends the year at 115 words per minute at 90% accuracy, that might be considered excellent growth and success for that student.
Proficiency is a measure of success that is consistent among all students. So a student starts the year at 130 words per minute, and ends the year at 120 words per minute, but the goal was 110 then he and his teacher would be marked a success. A student growing from 30 words per minute to 90 would not.
(Just a side note.. Using reading accuracy and fluency as truly meaningful data is it's own debate, but I figured this would be an easy to understand example)
Another issue is growth is just where they start versus were they end so it's pretty easy. In my state, proficiency was decided when they created the cut scores AFTER the students took the state test and they were graded. The cut scores were then created to make sure that a certain subset of students would be below proficiency. There was no way to know what the cut score would be because they changed every year and were not released until the results of the tests were released. This is why Franken doesn't like proficiency measures because they are arbitrary.