BTLS defines beginning public school teachers as teachers who began teaching in 2007 or 2008 in a traditional public or public charter school that offered any of grades K–12 or comparable ungraded levels. These teachers include regular full- and part-time teachers, itinerant teachers, and long-term substitutes, as well as any administrators, support staff, librarians, or other professional staff who taught at least one regularly scheduled class in the 2007–08 school year (excluding library skills classes). Beginning teachers who were sampled for, but who did not respond to, the 2007–08 SASS were not contacted to participate in the data collection of subsequent BTLS waves.

BTLS collects demographic data, information on respondents’ attitudes about the teaching profession and job satisfaction, as well as respondents’ reasons for moving to a new school, leaving the position of a pre-K–12 teacher, and returning to elementary or secondary teaching. BTLS can address questions such as the following:

• Are beginning teachers who received formal mentoring from their school or district less likely to leave the profession or change schools in the first few years of their teaching career?
• Do mobility rates of teachers, both within and outside of school districts, change over time?
• Why do teachers leave the teaching profession, and what factors have greater importance at various stages in their careers and lives?
• What proportion of teachers return to teaching after a break in their teaching career?
• What motivating factors bring former teachers back to the profession?

The BTLS dataset has at least one set of weighting variables for each wave of data, and each set has two types of weighting variables—the weight and the associated replicate weights. The weights are applied to each respondent and adjust for nonresponse and oversampling so that estimates represent the entire population, rather than just the sample population. The 88 replicate weights are used as a set to generate standard errors for estimates. There are a maximum number of four sets of weights for any given wave. Further information regarding the weights is available in the restricted-use data file documentation.

The first release of restricted-use BTLS data was in September 2011 and contained preliminary data from the first, second, and third waves of data. The final BTLS dataset contains five waves of data and was released in March of 2015. There are no plans to release public-use data files.

Due to the longitudinal nature of BTLS, data collected in latter waves were used to adjust previously missing, imputed, or inaccurate values. Thus, data collected in the fourth and fifth waves sometimes led to changes in first, second, or third wave data. In addition, respondents initially thought to be eligible for BTLS (i.e., met the definition of a beginning teacher) were sometimes determined to be out of scope in later waves. This occurred when it was determined that the teacher did not begin teaching at the elementary or secondary level in 2007 or 2008 or if the teacher did not teach a regularly scheduled class in the 2007–08 school year. These cases were removed from the data file and their initial weight is redistributed among the remaining cases.