Law ruins your life
Another day, another newspaper headline that automatically kicks in a legal response rather than anything else.
So our beloved tabloid (layout) The New Paper has as their headlines something about how a mother had changed (presumably unilaterally) her daughter's, age 9, surname to her own from her husband. The upset father is now suing all and sundry including the school and MOE. Now mind you, I have not read this report so the following analysis might be entirely wrong but I figure it shouldn't be too difficult to cover most conceivable (and probable) bases so it should be fairly accurate. In fact, the set of facts that shall be covered in the case below is so much more clearcut than the one listed in TNP that if that hadn't, there is nearly no possibility of there being a different outcome this time round.
As an aside, the reason law ruins your life is not only do you view this as a legal issue but specifically through the prism of family law (there are some rather fascinating constitutional issues about surnames but that tends to be in Japan and South Korea for various cultural reasons) as opposed to simply being a human-interest story.
The case that we are primarily interested in is a decade old case of L v. L,  1 SLR 222 (don't worry about the citation it's for the lawyers who can actually be bothered and have the access to look up the case). The proposition/legal rule that can be derived from this case is that a parent cannot unilaterally change the surname of the child i.e. without the consent of the other parent. This is because for various reasons, the change of a surname is held to be a "serious matter", as serious and important as taking the child out of Singapore for more than a month without the consent of the other parent (parental kidnapping). Anyway, the facts of the case were that the parents were divorced, the mother had sole custody and decided to change the surname of her daughter to the man she was about to marry. The father claimed that this act was unlawful and wanted a reversal of the change to be mandated by the court. Without g0ing into the decision of the Family Court and the High Court, the important part is that the Court of Appeal agreed, held that this was actually actionable and that a remedy would be granted.
Two thing of significance: 1. the mother actually had sole custody, which technically means she has sole authority (this has been strongly militated by judicial decisions) and there was absolutely no statutory prohibition against sole guardian changing name of the charge/ward. 2. the court found that the father was a caring father who was interested and concerned as to his child's well-being.
The second point is of relevance because of this later case of Khor Bee Imm v. Wong Tee Kee,  1 SLR 101 which also involved mother unilaterally changing surname of child, except that in this case, there was no court order for the reversal of the change. The reason simply was that it was not in the best interest of the child in this case to change his surname back. The father in this case was not as intimately involved nor as concerned with the well-being of the child. Furthermore, the child was not a young girl but a young man of 17 who had been with the changed surname for a good number of years, was known as such, had no desire to change it back, and comfortable with it. Furthermore he told he judge that he had no relationship with the biological father seeking the reversal.
So to iterate, you need the other parent's consent or you need a fairly exceptional set of facts and time to create some form of quasi-estoppel i.e. you are prevented from essentially going back on your "consent" to the surname change. It is quasi because legal estoppel can actually be enforced i.e. whereas this is merely a consideration that the judge will probably take into account.
And Now You Know (go google it). Peace