Teachers of English to Speakers of Other Languages (TESOL) assume different roles amongst which is leadership. To lead effectively, they need to possess some significant awareness of the language in order to adequately respond to learners’ needs. One domain of awareness is the ability to distinguish between structurally similar, yet semantically different structures. This study set out to assess ESL teachers’ level of semantic awareness in view of establishing their readiness to meet learners’ needs within their Zone of Proximal Development (ZPD). The Follow-up Explanatory Research Design was used. Data on the cognitions of ESL teachers were elicited from a questionnaire survey while a test was used to quantify ESL teachers’ language awareness levels in the domain of semantics. The quantitative data from the test were analyzed using frequencies and simple percentages while the qualitative data were analyzed using the framework of Content Analyses. The findings reveal that though ESL teachers overestimate the level of their knowledge base in components that have a bearing on semantics awareness, a majority of them do not wield beyond a fundamental level of awareness as concerns applying that knowledge to differentiate the meanings of structurally similar pairs of sentences. It is therefore crucial for English language pre-service and in-service teacher training to seek ways of enhancing the professional knowledge base of ESL teachers especially in domains that are critical to establishing differences between pairs of sentences that tend to be similar.