They've been sent back to school as part of a Rwandan government drive to switch to English instead of French as the routine language of instruction for the nation's schoolchildren.
That's no easy task for teachers brought up speaking French in this former Belgian colony. They now find themselves having to brush up their English, or in many cases learn it from scratch.
Often they struggle to keep pace with their own pupils, the education minister, Charles Murigande, admitted in a recent interview.
"It's not the children you should be feeling sorry for, they are picking it up quickly," he said. "It's the teachers who are having difficulties."
Critics say the switch to English in education has been rushed through and was politically motivated, but Murigande said it was "a logical choice" given where Rwandans do business - he mentioned Dubai, Malaysia, China and Japan.
Such a change would be a challenge for any country, but it is particularly difficult for Rwanda, which had nearly to start from scratch after the 1994 genocide.
Many teachers were among the dead when 800,000 people, mainly Tutsis, were slaughtered in the central African nation.
Afterwards, school buildings, books and equipment were all in short supply as Rwanda struggled to rebuild itself.
The situation has improved since then. In 2008, 53 per cent of children passed their primary leaving exam, up from just 24 per cent in 2000.
Progress is restricted by large classes, a shortage of qualified teachers, high drop-out rates and, in many cases, difficult home conditions.
Now, 15 months after the switch to English was announced in October 2008, many pupils appear to have taken to it with ease.
"Before, I used to like French," said 12-year-old Albert Mihigo cheerfully, as his friends nodded in agreement. "But since they started teaching us in English, I've forgotten French."
So at Kacyiru 1, a series of low-rise red-brick buildings around a beaten earth yard, teachers brought up on French are learning to decode English so they can pass it on to the nation's children.
Henry Kalanzi - resplendent in an orange silk waistcoast - claims the 45 teachers he is training can now "communicate, organise some dialogue on their own and prepare lessons in the English language".
But he admits his class is mixed, with some complete beginners and others who already master English.
"They are picking (up English) but one month is not a lot," added Kalanzi, 25. "When they go back to their classes there will be no follow-up."
Rwanda's teachers are not well paid and many in the state sector have just seen their working day doubled with the introduction of a double shift, where they teach one class in the morning and another in the afternoon.
English training for many teachers has been limited to just one month. Many admit to learning as they go along.
"As we teach, we learn at the same time," said Assinophol Nyabenda, one of those at Kacyiru 1.
That feeling was shared by teacher trainees at Kimihurura primary school a couple of kilometres (one mile) away.
"Last year the children were starting to understand. Gradually the teachers are understanding more, and the children too," volunteered Kalisa Byiringiro, 21.
"Twenty days to master a language is not enough, but we've been given the basics," said Jean Jabo, who at the age of 55 has a whole career of teaching history and geography in French behind him.
Until October 2008, education in Rwanda was dispensed in a mixture of its three official languages: local Kinyarwanda; French, which is spoken mainly by an educated elite; and English, which was added in 1994.
Outside major towns, a vast majority speak only Kinyarwanda.
Part of the government's rationale for the switch was that it intended to join the Commonwealth club of mainly former British colonies, which it did in late 2009.
But the reform was announced during a rupture in relations between France and Rwanda, leading some commentators to speculate that the motivation was at least in part political.
It came after a French judge issued arrest warrants for nine officials in President Paul Kagame's entourage. They were accused of shooting down the plane carrying former leader Juvenal Habyarimana - the event widely considered to have caused the 1994 genocide.
Diplomatic relations resumed in November 2009, and Louise Mushikiwabo, the foreign minister, has insisted that the expansion of English will not take place at the expense of French.
The move affects only the education system - French continues to be used, alongside English, by an educated elite, and is still offered as a subject at school.
"The transition had already been in the pipeline for some time," said Iris Uyttersprot, education advisor with development agency the Belgian Technical Cooperation.
"The actual timing of the announcement may have been political," she added, "it came as a surprise to many and was initially enforced too quickly."
She said at first there was little planning and preparation but that "this seems to have been corrected now".
Still, some critics fear the switch to English may mean children from poor and medium-income families fare even worse in school.
"It's something that should have been done over a period of say 10 years," complained one father of four."My son, who was studying in French before, now comes home from school and tells me he has been correcting his teacher's mistakes in English.