What is the relationship between student academic performance and watching TV and video on school nights?

Why is this question important? Students have limited time to divide between activities on school days. Knowing how TV and video watching is generally related to school performance can help them and their parents make informed decisions.

See further discussion below.

Source: National Assessment of Educational Progress Data Explorer
http://nces.ed.gov/nationsreportcard/lttdata/

Results: Strong correlation between NAEP Reading Long-Term Trend Scale Score and TV/video watching on school nights, with more hours watching corresponding to lower scores. General trend toward lower scores after 1994, even for students who watch little or no TV or video on school nights. Score differences dropping between 1994 to 2008 for students with zero to 2 hours of watching per night. Small improvement in scores between 2004 and 2008 for students with 1 to 4 hours watching per night.

Implications: Generally less TV and video watching on school nights corresponds with better reading scores. Little TV/video watching does not counter the general trend of deteriorating reading scores. It is important to note that causation cannot be inferred from these data.

Authors:  National Assessment of Educational Progress, Institute of Education Sciences, National Center for Education Statistics, U.S. Department of Education
http://nces.ed.gov/nationsreportcard/ltt/sampledesign.asp

Publisher: National Assessment of Educational Progress, Institute of Education Sciences, National Center for Education Statistics, U.S. Department of Education

Study Description: The NAEP long-term reading assessment was designed to measure students' ability to 1) locate specific information, 2) make inferences base on information in two or more parts of a passage, and 3) identify the main idea in a passage. Students' comprehension was assessed with both multiple-choice and constructed-response questions. http://nces.ed.gov/nationsreportcard/ltt/what_measure_reading.asp

As part of the NAEP assessment, student questionnaires collect information on students' demographic characteristics, classroom experiences, and educational support. Teacher qustionnaires gather data on teacher background, training, and instructional practices (for grades 4 and 8). School questionnaires, completed by principals or assistant principals, gather information on school policies and characteristics. Questionnaires for students with disabilities or English language learners (SD/ELL), completed by special education or English language teachers, collect information about students who have disabilities or limited English proficiency. 

From approximately 27,700 students who took the reading assessment, NCES makes a multi-stage sampling of scores, first from representative geographies, then from representative schools, both public and nonpublic, then randomly selecting students within selected schools. http://nces.ed.gov/nationsreportcard/ltt/sampledesign.asp

Results from the long term reading assessment were grouped based on how students answered the background question, 'On a school day, about how many hours do you usually watch TV or videotapes outside of school hours?'
Possible answers were: None, 1 hour or less, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or more, Omitted(no answer).

Definitions:
NAEP = National Assessment of Educational Progress
NCES = National Center for Education Statistics
SD = Students with disabilities
ELL = English Language Learners

National Assessment of Educational Progress Data Explorer Variables:
Subject: Long-Term Trend Reading
Measure: Long-Term Trend scale
Age: 17
Jurisdiction: National
Years: 84, 88, 90, 92, 94, 96, 99, 04, 08
Factors Beyond School|Time use outside of school|Amount of TV/video watched on school day