The Livingston-based school, which provides education and support for secondary-age pupils with a range of additional support needs, have been working for the last four years to earn the coveted top award.
This has included developing the school garden, purchasing new gardening equipment and embedding garden-related pupil activities into the S1-3 curriculum.
Depute head teacher Alison Lindsay, who has led the project, explained: "We were so pleased to be awarded five-star status by the RHS after years of hard work by our pupils and staff.
"We have been submitting evidence each year for the past four years, achieving additional stars each time, but to reach the top five-star award is something special for us all. While Covid restrictions have hampered many school activities, the appreciation of nature and the benefits of being outside have only increased in Cedarbank school.
"Pupils now grow vegetables and more fully understand the effects of sustainable living. We have pupils in lead roles such as the apple tree supervisor who led an assembly on how a tree grows and the 'Frogateers' who supervise the wildlife area, show new pupils the frog population and promote their protection. In Outdoor Learning, pupils create structures, ponds and plant seeds.
"It also provides a good outlet for many pupils who show an interest or aptitude for gardening or outside working, to experience working in this area in conjunction our 'Developing the Young Workforce' agenda in school.
Cedarbank were also awarded a bronze plaque for the wildlife and food growing sections of their gardens in the West Lothian School Garden award scheme in 2019.
Executive councillor for education David Dodds added: "Congratulations to all the staff and pupils at Cedarbank on their RHS five-star award.
"It's a fantastic achievement, and a fitting reward for the years of work put in by everyone at the school."