A major study looking at 30 other studies over the past 15 years shows that teachers get better with experience, especially if they are in a supportive and collaborative environment and get to teach the same subject matter or age level repeatedly.
Or, ‘duh’: 5 weeks of training isn’t enough.
A money quote from the summary:
Based on our review of 30 studies published within the last 15 years that analyze the effect of teaching experience on student outcomes in the United States and met our methodological criteria, we find that:
1. Teaching experience is positively associated with student achievement gains throughout a teacher’s career. Gains in teacher effectiveness associated with experience are most steep in teachers’ initial years, but continue to be significant as teachers reach the second, and often third, decades of their careers.
2. As teachers gain experience, their students not only learn more, as measured by standardized tests, they are also more likely to do better on other measures of success, such as school attendance.
3. Teachers’ effectiveness increases at a greater rate when they teach in a supportive and collegial working environment, and when they accumulate experience in the same grade level, subject, or district.
4. More experienced teachers support greater student learning for their colleagues and the school as a whole, as well as for their own students.
Here is the full link: https://learningpolicyinstitute.org/wp-content/uploads/2016/06/Teaching_Experience_Report_June_2016.pdf