The study was implemented with 90 Grade 12 students from a rural upper secondary school in Kien Giang Province, Vietnam. The main objectives of this study were to explore the effects of instructional scaffolding on (English as a Foreign Language) EFL high school students' making references and guessing words' meanings in reading texts and to gain an insightful look into high school students’ attitudes towards EFL teacher’s instructional scaffolding namely questioning and modelling about making references and guessing words' meanings during reading lessons. The study was designed as an experimental study. A mixed method research was employed. Both quantitative and qualitative data were collected by exploiting three significant research instruments in terms of a pretest-posttest, a questionnaire and a semi-structured interview. The findings of the study showed that modeling and questioning greatly affected EFL high school students' English learning. In this particular case of Vietnamese context, modeling and questioning also influenced English vocabulary learning. (1) Both of these techniques increased students' ability to understand and use English vocabulary, (2) these two techniques could be scaffolded and used in learning English vocabulary, and (3) questioning and modeling had a positive impact on high school English learning environment.