Cuirfear síos ag tús an ailt, ar anailís earráidí a rinneadh ar earráidí coitianta sa Ghaeilge scríofa a bhí ag grúpa bunmhúinteoirí faoi oiliúint (n=80). Ag eascairt ón anailís ar earráidí, roghnaíodh ceithre spriocstruchtúr: na huimhreacha, an aidiacht shealbhach, na réamhfhocail shimplí is cúis le séimhiú ar chonsan agus an t-ainm briathartha d’idirghabháil foirm-dhírithe. Cuireadh cur chuige déaduchtach i bhfeidhm le dhá ghrúpa, agus cuireadh cur chuige ionduchtach-follasach i bhfeidhm le dhá ghrúpa (n=60), ar feadh caoga nóiméad sa tseachtain, thar thréimhse d’ocht seachtaine. Rinneadh iniúchadh sa staidéar seo, ar éifeachtacht an teagaisc fhollasaigh ar ghnóthachtáil na múinteoirí faoi oiliúint (n=60) ar na ceithre spriocstruchtúr. Fiosraíodh ach go háirithe, cé acu cur chuige follasach ab éifeachtaí, cur chuige déaduchtach nó cur chuige ionduchtach-follasach, le forbairt a dhéanamh ar léireolas na mac léinn ar na struchtúir. Cuireadh triail ghramadaí ar na mic léinn ag Céim a hAon (roimh an idirghabháil); ag Céim a Dó (díreach i ndiaidh na hidirghabhála); agus ag Céim a Trí (seacht seachtaine i ndiaidh na hidirghabhála). Léiríodh difríocht shuntasach le tomhas mór éifeachta i ngnóthachtáil na mac léinn ar na ceithre struchtúr, ó Céim a hAon go Céim a Dó, gan ach titim bheag sna torthaí ag Céim a Trí, leis an dá chur chuige follasacha. Tháinig sé chun solais sa taighde gur tháinig feabhas ní ba mhó ar struchtúir áirithe i ndiaidh an teagaisc fhollasaigh, agus gurbh é struchtúr an ainm bhriathartha an struchtúr ba dhúshlánaí as na ceithre struchtúr do na mic léinn. Tugadh le fios gur chothaigh giniúint an eolais fhógraigh dúshlán ar leith do na múinteoirí faoi oiliúint. Tugann torthaí na hanailíse earráidí léargas suimiúil ar na hearráidí ba choitianta sa Ghaeilge scríofa a bhí ag grúpa amháin bunmhúinteoirí faoi oiliúint. Tá sé mar aidhm ag an bpáipéar túsphlé a spreagadh ar eolas gramadúil bunmhúinteoirí faoi oiliúint agus ar theagasc na gramadaí sna hinstitiúidí oideachais. Results from an error analysis of common errors in written Irish from a sample of student primary school teachers (n=80) are presented at the beginning of the paper. Arising from the analysis four target structures: numbers, the possessive adjective, simple prepositions which lenite consonants and the verbal noun clause, were selected for a form-focused intervention. A deductive approach was implemented with two groups, and an explicit-inductive approach was implemented with two groups (n=60), for fifty minutes per week, over an eight week period. This study examined the effectiveness of explicit grammar teaching on the student primary teachers’ achievement on the four target structures. The study investigated in particular, which explicit approach, a deductive or an explicit-inductive approach, would be most effective in developing the students’ explicit knowledge of target forms. An Irish grammar test was administered to students at Time One (before the intervention); at Time Two (immediately following the intervention); and at Time Three (seven weeks after the intervention). Results revealed a significant difference, with a large effect size, in student achievement on the four target structures from Time One to Time Two, with a slight decrease in scores at Time Three, for both explicit approaches. The study showed that student achievement increased more on particular structures, as a result of the explicit teaching, and that the verbal noun clause was the most challenging of the four structures for the students. Results also indicated that the production of declarative knowledge posed a significant challenge for the student teachers. Results from the error analysis provide an interesting insight into the common grammatical errors in written Irish, of one sample of student primary teachers. It is intended that this paper will initiate dialogue about the grammatical knowledge of student primary teachers and the teaching of grammar in Institutes of Education.