A growing body of research examines attitudes towards English varieties from an impressionistic perspective, but relatively few studies investigate attitudes towards specific standard and variant grammatical features. This study explores the language attitudes of Thai university students and teachers towards standard grammar and its variation in present-day English. The study adopted an online questionnaire which consisted of 15 pairs of sentences, with each pair containing two corresponding grammatical forms: standard and variant. Respondents chose standard and/or variant forms and provided reasons for their grammar choices. The responses and reasons were analysed using statistical and content analysis methods respectively. The analyses of acceptability responses by 182 students and 182 teachers revealed that the students were inclined to choose variant forms while the teachers were favourably disposed to both standard and variant forms. With respect to reasoning, both groups of the respondents overwhelmingly cited standard grammar rules to justify their preferences. However, they were significantly different in that while the teachers described the variations in grammatical forms, the students employed analogies with similar grammatical patterns. The overall results indicate that the respondents remain influenced by the standard language ideology. The results also suggest that the teachers tend to use their norm-providing roles to regulate standard forms while the students generalise rules of thumb to simplify and regularise prescriptive irregular usages. This article argues that grammar learning and teaching should address language variation and variant linguistic forms from a descriptive perspective.