The school crest is made up of three design elements in the shape of the letters G, D and L, which form the acronym of the school name 'GDL'. G and D are arranged close together to form 'GD', the short form of the word 'Good' to signify Greendale Secondary is a Good school. The upward orientation of the letter 'D' symbolises the school's aspiration to excel. The design of the letter 'L' resembles a springboard which symbolises the school's commitment to value-add to the development of the students and propel them to greater heights.
Red, yellow and orange in the school crest symbolise the school's passion, energy, joy, and enthusiasm for learning. Green is associated with the rustic and green surroundings.
The brown diamond ring and school motto were subsequently added to the original design, in 2008. The brown ring symbolises the school's desire to provide a safe environment that is conducive for teaching and learning. The school motto emphasises the commitment of staff and students to Serve, Lead and Excel.