The study examines the effect of teaching strategies to improved writing of students in the tertiary level. Specifically, three teaching approaches--the use of modelling, grammar-based, and information element-focused--were tested on their effect on the writing of annotated bibliography in three research classes at a university in Manila. Initially, 125 participants from the three classes were administered a pre-test to check their writing proficiency. Each class was then exposed to a particular teaching approach. All participants were instructed to write an annotated bibliography right after. All annotated bibliographies were rated using one assessment scale. Descriptive statistics as well as Pearson correlations were obtained. Using One-Way ANOVA, the study revealed that the modelling approach has the most marked effect on the success of annotated bibliography writing. The findings in the study may be used by teachers to guide them in their research writing course. The study has impact on the way educators should present their learning materials for the students' more improved writing of annotated bibliography.