An AR-enhanced contextualized learning was developed to facilitate EFL learning for junior high school students. A preliminary study was conducted to examine the effects of levels of prior knowledge (low vs. high) on participants' learning effectiveness and attitude toward the implemented AR-enhanced theme-based contextualized learning. The analysis suggested that prior knowledge affected participants' learning from the experimental AR-enhanced learning. With the advantage in prior knowledge, the high prior knowledge learners outperformed the low prior knowledge learners both in comprehension and application performance and possessed higher degrees of confidence, preferences, deep learning and learning strategy but with lower degrees of anxiety. It was suggested that suitable learning supports need to be considered to adapt to EFL beginners' levels of prior knowledge in order to facilitate their learning.