Few topics in SLA are as contentious as grammar teaching. Differences in opinion persist about whether, what, and when grammar should be taught explicitly. While most SLA researchers now agree that acquisition is primarily a subconscious process, there is a good deal of empirical evidence suggesting that it can be accelerated through explicit teaching, provided forms are presented in a way that respects the natural order of acquisition. Among proponents of explicit instruction, few believe it is feasible or desirable to teach all forms, but there is great disagreement regarding which forms should be taught. This advice provides little practical direction for practitioners and policymakers wondering whether and when to teach a particular form explicitly in their classrooms. This article proposes a framework for a tool called the Implicit/Explicit Knowledge Axis which could be developed to provide critical guidance on the matter.