Sibling rivalry: It is thought that the children benefit from the age gap because parents have more time to invest in them

Forget expensive educational DVDs and private tutors, the secret to smart children could be as simple as giving birth to them two years apart.

Researchers who studied thousands of children found a two-year gap to be optimum in boosting brain power.

Any shorter, and the reading and maths skills of the older child dipped.

The effect was strongest between the first and second-born, but siblings in bigger families also benefited.

The theory comes from Kasey Buckles, an economist whose own children are, rather fortunately, just over two years apart in age.

She said it is likely that the difference in academic achievement is linked to the time and resources parents can invest in a child before a younger sibling arrives.

However, waiting more than two years did not increase the advantage, the Journal of Human Resources will report.

Siblings with a two-year spacing include Albert Einstein and sister Maja, and Lord Attenborough and younger brother David.

Kasey Buckles, who lead the study told the Sunday Times: 'We believe this is the first time anyone has established a casual benefit to increase the spacing between siblings.'

The study also showed that gaps between children in larger families was also beneficial.

Buckles told the newspaper: 'The two year gap is significant because the early years are the most important in a child's development so dividing your time when the child is one is more harmful than dividing it when the child is already at school.'

The effect was more pronouncedin families with lower incomes, as those with more money could spend to compromise for lack of time.

忘了昂贵的教学光碟和家教吧，想让孩子聪明，秘诀很简单，就是第一胎和第二胎的出生相隔两年。

研究人员研究了成千上万名小孩后发现，要增进小孩的智力，最好是在两胎间相隔两年。

间隔时间再短的话，年长的孩子的阅读和数学技能都会下降。

这一影响在第一胎和第二胎孩子身上最为强烈，不过大家庭中有兄弟姐妹的孩子也会因此而收益。

得出这一理论的是经济学家凯西 巴克尔斯，挺幸运的是，她自己的小孩的出生间隔时间正好是两年多一点。

她说，学习成绩的差别可能和父母在更小的孩子出生之前能够投入到孩子身上的时间和资源有关。

不过，《人力资源杂志》却报道说，超过两年后再生第二个小孩并不会让孩子的智力更有优势。

兄弟姐妹出生间隔两年的例子有阿尔伯特 爱因斯坦和妹妹玛雅，还有艾登堡爵士和弟弟戴维。

这一研究的领头人凯西 巴克尔斯告诉《星期日泰晤士报》说：“我们相信这是首次有人提出同胞出生的间隔时间增大能够带来附加的好处。”

该研究还显示，在大家庭中，孩子的年龄间隔大也是有益处的。

巴克尔斯告诉《星期日泰晤士报》说：“两年的出生间隔很重要，因为孩子成长过程中的头几年最重要，所以在孩子一岁的时候分散照顾时间比孩子入学后再分散照顾时间更有害。”

这一影响在低收入家庭中更为显著，因为那些富裕的家庭可以用钱来弥补时间的不足。

Vocabulary:

dip: 下降

pronounced: 明显的，显著的