Teaching Secondary Students to Write Effectively

Internal validity of supporting evidence. 

The studies have strong internal validity. Six 

were randomized controlled trials (RCTs) with 

low sample attrition that meets WWC group 

design standards without reservations.

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Three studies were RCTs with high attrition, 

compromised random assignment, or differ-

ent assignment probabilities not accounted 

for in analysis. These studies demonstrated 

baseline equivalence and meet WWC group 

design standards with reservations.

120

 Two 

studies were quasi-experimental designs 

(QED) that meets WWC group design stan-

dards with reservations.

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