The Blairgowrie High School SA Premium Tartan Kilt likely refers to a kilt made from the official tartan of Blairgowrie High School in Johannesburg, South Africa. Here's a description of the tartan itself:

• Designed in 1989 by Arthur Mackie of Strathmore Woollen Co.
• Variation of the Murray of Atholl tartan with a distinct difference
• Has an extra black line running alongside the existing blue lines (five black lines instead of four)
• Considered a "premium" tartan likely due to the use of high-quality materials or weaving techniques

Since it's a premium kilt, it's probably made from:

• Heavier weight tartan fabric (like a 16oz or 18oz fabric) for a more structured drape

Unfortunately, I couldn't find specific details about the kilt itself, such as pleating style (knife pleats, box pleats) or hardware (buckles, straps).