Student teaching is intended to be the culminating experience of a teacher's preparation. It's typically a fall or spring semester commitment. Over the last few years, there's been a steady drum beat for turning it into a full year. And, as I've witnessed numerous times, it's an idea that plays very well with all sorts of audiences, and is met with the same approving nods and applause as smaller class sizes. What's not to love?

Except at scale it's not a particularly practical idea nor is it even a good one. 

Let's examine its practicality. Requiring a full-year of high quality student teaching effectively means placing far too many student teachers in less-than-ideal classrooms. Just as California and Florida learned when they reduced class sizes, the supposed learning benefits are quickly undermined when the classroom teacher is weak. There is nothing magic about spending a full year instead of a half year under the tutelage of a weak teacher. 

We estimate that of the nation's 3+ million classroom teachers, only about 1 in 25 is likely to have all of the qualifications needed to mentor a student teacher: has the necessary experience (at least 3 years by most state laws), is highly effective (in the upper quartile among their peers), has the ability to mentor an adult (lots of great teachers make poor mentors), and, most importantly, has the willingness to take on the responsibility of a student teacher year in and year out. For many teachers, particularly great teachers, having a student teacher in their classroom is disruptive to the real work at hand. A 1:25 ratio adds up to about 120,000 qualified, willing teachers across the nation. 

That's not even enough qualified teachers to cover a semester's worth of student teaching, 30,000 short of the current level of 150,000 placements. No wonder so many student teachers don't get the high quality experience they need. Double the length and the quality deficit is irremediable.
But what's more important—and ironic—than the impracticality of the year-long push is that its implementation means that teacher candidates will be even less likely to get the foundational training they need. 

For as valuable as student teaching is, it should only come after teacher candidates have first had lots of time and practice without real children serving as their guinea pigs. Think of the piano student who must practice scales, or the football player who does the same drills over and over, or the medical student who learns from simulations or cadavers before encountering real live patients. Why would teaching be exempt from this kind of mastery building, in which teachers must practice the instructional strategies most likely to lead to success?

I recently shared a podium with SUNY Chancellor Nancy Zimpher, once the education dean at Ohio State. She also rejects this push for a full year of student teaching, vehemently insisting that programs should instead require advanced skills building before placing student teachers in front of real children. 

Some teacher prep programs, both traditional and non-traditional, are ramping up just such practice opportunities using video, virtual classrooms, role playing or simulations. Candidates who emerge from these intense practice sessions in which individual skills are rehearsed to mastery will arrive at student teaching far more competent and ready to teach children.