Value-added modeling (VAM), one class of statistical models used to estimate individual teacher's or school's contribution to student achievement based on student test score growth between consecutive years, has become increasingly popular in the last decades. Despite the increasing popularity of VAM, many researchers are concerned about the quality of value-added (VA) scores as a measure of teaching and call for more research on VAM. One area of VAM that needs more research is about teacher spillover effects (TSEs). In this study, the author studied TSEs across four types of teachers, including math, ELA, science, and social studies, on student achievement in each of the four subjects. When estimating teachers' value-added scores, the author used models similar to what is commonly used in the practice, which estimate teachers' annual effects and control for teacher or classroom aggregates of student variables. By using models that are commonly used in the practice, the author expected to understand the magnitude of TSEs and the consequence of ignoring such effects for estimating own-subject teachers' value-added scores in the common practice. Specifically, the author addressed the following two research questions: (1) Do TSEs exist across teachers of math, English Language Arts (ELA), science, and social studies on any of the four subjects at the middle school level?; (2) If so, how does controlling for TSEs affect the relative stance and variation of own-subject teachers' effects? Data came from an urban school district in the Southern United States. Data used for analysis followed students at grades 6-8 and their math, ELA, science, and social studies teachers from 2006-07 to 2008-09. Results from both types of value-added models showed consistent evidences of teacher spillover effects at all three grade levels in middle schools, especially from ELA teachers to students' achievement on the other three subjects. Consistent with most prior studies on teacher spillover effects, this study found evidence of TSEs. Tables are appended.