だけのことはある is a grammar structure consisting of the particle だけ, の, こと, は, and the う-Verb ある. It is used when indicating that something about (A) is ‘as expected’, or ‘not surprising’. As a literal translation, it can be thought that the meaning is close to ‘just in that it is (A), (B)’, and expresses that simply because (A) is (A), (B) is to be expected.
だけのことはある will often appear with other words that add emphasis to the expectation of (A), such as さすが, やはり, or やっぱり.
This grammar pattern may be seen following verbs, い-Adjectives, な-Adjectives or nouns. な will be required after な-Adjectives.

• 娘（むすめ）が空手（からて）の大会（たいかい）で優勝（ゆうしょう）した。さすがに1年間（ねんかん）毎日（まいにち）稽古（けいこ）に行（い）っていただけのことはある。
  My daughter won a karate competition. As expected, she has been going to practice every day for a year.
• 田中（たなか）くんは体力（たいりょく）もあるし動（うごき）きもテキパキしている。やっぱり若（わか）いだけのことはあるな。
  As expected from someone as young as Tanaka-kun, he is physically strong and moves quickly.
• あのホテルのサービスはとても良（よ）かったし、朝食（ちょうしょく）と夕食（ゆうしょく）もものすごく美味（おい）しかった。やっぱり有名（ゆうめい）なだけのことはある。
  The service at that hotel was very good and the breakfast and dinner were extremely delicious. As expected from how famous that place is.
• 高橋（たかはし）先生（せんせい）が書（か）く漢字（かんじ）はものすごく綺麗（きれい）だ。さすが習字（しゅうじ）の先生（せんせい）だけのことはある。
  Takahashi-sensei's kanji writing is extremely beautiful. As expected from a calligraphy teacher.

In the case of nouns and な-Adjectives, it is also possible to see だっただけのことはある when highlighting that some particular result is not surprising.

• あの政治家（せいじか）はとても信頼（しんらい）されている。さすが昔（むかし）から正直（しょうじき）だっただけのことはある。
  As expected from a politician that has been honest for years, he is very trusted.
• 鈴木（すずき）さんは６０歳（さい）なのにムキムキだ。昔（むかし）ボクサーだっただけのことはある。
  As expected from someone who used to be a boxer, Suzuki-san is very muscular even though he is 60 years old.